External Authentication via Apache Webserver

I want to use the Webserver Basic Authentication as authentication method for the login to icingaweb.

For this purpose, I wrote into /etc/icingaweb2/authentication.ini the following 2 lines:

[root@tlin40 ~]# cat /etc/icingaweb2/authentication.ini
backend = “external”

and into /etc/httpd/conf.d/icingaweb2.conf I added in the <Directory “/usr/share/icingaweb2/public”> directive:

AuthType Basic
AuthName “Icinga Web 2”
AuthUserFile /etc/icingaweb2/.http-users
Require valid-user

For a first testing attempt, I added only a single userid into the users file:

[root@tlin40 ~]# cat /etc/icingaweb2/.http-users

I followed the instructions in https://icinga.com/docs/icingaweb2/latest/doc/05-Authentication/ .

If I want to login into the Web Application http://tlin40.mainz.de.ibm.com/icingaweb2/authentication/login , the following error messages is displayed and I am unable to login:
“You’re currently not authenticated using any of the web server’s authentication mechanisms. Make sure you’ll configure such, otherwise you’ll not be able to login.”

I am using the OS “Red Hat Enterprise Linux Server release 7.7 (Maipo)” and icinga2-2.11.3-1.el7.icinga.x86_64 with icingaweb2-2.7.3-1.el7.icinga.noarch .